The present invention relates to an arrangement and method for the tensioning and adjusting of a camshaft chain drive and, more particularly, to an arrangement by means of which a camshaft of a piston internal-combustion (IC) engine drives a second camshaft, with the relative rotational position of the camshafts being changed by adjustment of the chain with a hydraulic piston.
A tensioning and adjusting arrangement is described in P 40 06 910.9. A hydraulic tensioning device for a chain enclosing the two camshafts of an internal-combustion engine comprises two hydraulic pistons which are concentrically guided in one another. A spring, which is centrically arranged between the hydraulic pistons, shifts the hydraulic pistons in opposite directions with respect to one another and places the tensioning shoes fastened to their ends against the chain. When the hydraulic pistons are acted upon by hydraulic pressure, the tensioning arrangement is shifted transversely with respect to the chain so that the relative rotational position of the inlet camshaft to the outlet camshaft will change by the shortening of the loose end and the lengthening of the load end. Thus, the control time of the inlet valves is changed. A control slide valve, which is longitudinally slidable via an electromagnet and controls the pressure feeding ducts to the tensioning device, is used for controlling the hydraulic pressure.
It is a object of the present invention to simplify the known tensioning and adjusting arrangement and method, and thereby also reduce its manufacturing costs.
The foregoing object has been achieved by using engine oil as the hydraulic fluid. Since the engine oil pressure rises with the rotational speed of the engine, the adjusting arrangement can be actuated as a function of the rotational speed of the engine without requiring an electromagnet. In addition, the external control of the electromagnet may also be eliminated. Hence, the arrangement can be manufactured at low cost.
In a first embodiment of the present invention, the engine oil pressure directly affects the hydraulic piston which, from the direction of the other side, is braced by a spring. An equilibrium occurs at the hydraulic piston between the product of the piston surface times engine oil pressure and the spring force acting from the other side. Since the engine oil pressure rises with the rotational speed, a specific engine rotational speed corresponds to a defined deflection of the hydraulic piston and thus to a specific adjustment of the inlet camshaft to the outlet camshaft.
In a second embodiment of the present invention, the engine oil pressure is in contact with a control member which is braced by a spring and can be moved longitudinally in a housing bore and from which a duct leads to the hydraulic piston. As the engine oil pressure increases, the control member is slid farther along until it exposes the duct to the hydraulic piston. Starting here, the full oil pressure then affects the hydraulic piston and shifts it into the maximal adjusting position. If the oil pressure is lowered again, the hydraulic piston returns to the starting position. As tests have shown, this simple 2-point control is capable of significantly increasing the engine torque in the lower rotational speed range and of increasing the performance.